For allowing users to operate keyboards in a dark or dim environment, some keyboards with light sources such as light emitting diodes (LED) have been introduced into the market. The light sources may provide light beams to illuminate the keyboards. The keyboards with the illuminating functions are also referred as illuminated keyboards. By using the illuminated keyboards, the users can easily identify the characters or the symbols marked on the keys of the illuminated keyboards.
FIG. 1 is a schematic view illustrating a conventional illuminated keyboard. As shown in FIG. 1, the conventional illuminated keyboard 10 comprises a key structure 11, a membrane switch board 12, a backlight module 13, and a bottom plate 14. The membrane switch board 12 comprises an upper wiring plate 15, a lower wiring plate 16, and a partition plate 17. The backlight module 13 comprises a light-shading plate 18, a light guide plate 19, a reflecting plate 20, and a light source L.
The key structure 11 is disposed over the membrane switch board 12 to be depressed by the user. When the key structure 11 is depressed, the membrane switch board 12 is electrically conducted to generate a key signal. The detailed structures of the membrane switch board 12 will be illustrated as follows.
In the membrane switch board 12, the upper wiring plate 15 comprises an upper circuit layer 151, and the lower wiring plate 16 comprises a lower circuit layer 161. The upper circuit layer 151 and the lower circuit layer 161 are circuit patterns that are made of an electrically-conductive material. The upper wiring plate 15 is disposed over the lower wiring plate 16. The partition plate 17 comprises plural perforations 171. Moreover, the partition plate 17 is arranged between the upper wiring plate 15 and the lower wiring plate 16 for preventing erroneous contact between the upper wiring plate 15 and the lower wiring plate 16.
As the key structure 11 is depressed, the upper wiring plate 15 is subjected to deformation. Consequently, the upper circuit layer 151 of the upper wiring plate 15 is penetrated through the corresponding perforation 171 of the partition plate 17, and the upper circuit layer 151 of the upper wiring plate 15 is contacted with the lower circuit layer 161 of the lower wiring plate 16. Under this circumstance, the electrical connection between the upper circuit layer 151 and the lower circuit layer 161 results in the key signal.
The backlight module 13 is disposed under the membrane switch board 12 for illuminating the key structure 11. The backlight module 13 comprises the light-shading plate 18, the light guide plate 19, the reflecting plate 20, and the light source L. The light guide plate 19 is located at a side of the light source L for transferring the light beam, which is emitted by the light source L. The reflecting plate 20 is disposed under the light guide plate 19 for reflecting the light beam to the light guide plate 19, thereby increasing the light utilization efficacy of the light source L. The light-shading plate 18 is disposed over the light guide plate 19. Moreover, the light-shading plate 18 comprises a light-transmissible region A and an opaque region B. The light beam is allowed to be transmitted through the light-transmissible region A of the light-shading plate 18. The opaque region B of the light-shading plate 18 is used for shading the light beam in order to prevent the light beam from being transmitted to any place where the light beam is not needed. Consequently, the light leakage problem can be eliminated. The bottom plate 14 is disposed under the backlight module 13 for supporting the key structure 11, the membrane switch board 12 and the backlight module 13.
By means of the light guide plate 19, the reflecting plate 20 and the light-shading plate 18 of the backlight module 13, the light beam from the light source L can be uniformly transferred to each key structure 14. Consequently, the illuminated keyboard 10 has the backlighting function, the number of the light sources L is reduced, and the light leakage from the key structure 11 will be minimized. Under this circumstance, the illuminated keyboard 10 is cost-effective and aesthetically pleasing. However, the conventional illuminated keyboard 10 still has some drawbacks. For example, due to the thicknesses of the light-shading plate 18, the light guide plate 19 and the reflecting plate 20, the arrangement of the backlight module 13 under the membrane switch board 12 may increase the overall height of the illuminated keyboard 10. Consequently, it is difficult to further reduce the thickness of the illuminated keyboard 10.
Therefore, there is a need of providing an improved illuminated keyboard in order to eliminate the above drawbacks.